Inspection method and inspection apparatus using electron beam

ABSTRACT

An inspection method and an inspection apparatus using an electron beam enabling more detailed and quantitative evaluation at a high throughput level. The method comprises the steps of irradiating, based on previously prepared information concerning a defect position on the surface of a sample, the defect and its vicinity with an electron beam a plurality of times at predetermined intervals; detecting an electron signal secondarily generated from the sample surface by the electron beam; imaging an electron signal detected by the previously specified n-th or later electron beam irradiation; and measuring the resistance or a leakage amount of the defective portion of the sample surface in accordance with the degree of charge relaxation by monitoring the charge relaxation state of the sample surface based on the electron beam image information.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inspection method and an inspectionapparatus using an electron beam, both of which inspect a sample such asa semiconductor device having micro-fabricated patterns, a substrate, aphotomask (a mask having patterns formed thereon, which is used forexposing patterns on a substrate), and a liquid crystal plate.

2. Description of the Related Art

Semiconductor devices such as memories and microcomputers used forcomputers, etc. are manufactured through the repetition of transcriptionprocesses such as exposing, lithographing, or etching patterns such ascircuits, which are formed on photomasks. In the manufacturing processof semiconductor devices, the manufacturing yield is greatly affected byseveral factors. These include whether or not the results of thelithography process, etching process, or other processes involved aresatisfactory. Yield is also affected by the presence or absence offoreign matter of the like. Therefore, in order to detect early or inadvance the occurrence of abnormalities or defects, patterns on asemiconductor wafer are inspected at the end of each manufacturingprocess.

As one example of a method for inspecting defects present in a patternon a semiconductor wafer, an optical visual inspection apparatus hasbeen put into practice, wherein the comparison of patterns is performedusing optical images obtained through light irradiation of asemiconductor wafer. However, as circuits have miniaturized (micro)patterns and complicated shapes, and as materials used for circuits havebecome diversified, it is difficult to detect these defects usingoptical images. Thus, a method and an apparatus for inspecting a patternusing an electron beam image that has higher resolution than an opticalimage have been put into practice.

Known are technologies disclosed, for example, in JP Patent Publication(Kokai) No. 59-192943, JP Patent Publication (Kokai) No. 5-258703,Sandland, et al., “An electron-beam inspection system for x-ray maskproduction,” J. Vac. Sci. Tech. B, Vol. 9, No.6, pp. 3005-3009 (1991),Meisburger, et al., “Requirements and performance of an electron-beamcolumn designed for x-ray mask inspection,” J. Vac. Sci. Tech. B, Vol.9, No. 6, pp. 3010-3014 (1991), Meisburger, et al., “Low-voltageelectron-optical system for the high-speed inspection of integratedcircuits,” J. Vac. Sci. Tech. B, Vol. 10, No. 6, pp. 2804-2808 (1992),Hendricks, et al., “Characterization of a New Automated Electron-BeamWafer Inspection System,” and SPIE Vol. 2439, pp. 174-183 (20-22 Feb.,1995).

In order to achieve high throughput and highly accurate inspections inline with the increase of wafer bore diameter and the miniaturization ofcircuit patterns, there is a need to obtain a high SN image at very highspeeds. To this end, the number of electrons emitted through the use ofa larger beam, with a current 1,000 times or more (100 nA or more)greater than that of an ordinary scanning electron microscope(hereinafter referred to as an SEM), should be preserved to ensure themaintenance of a high SN ratio. Further, it is essential to detectsecondary electrons generated from a substrate and reflected electronsat high speeds and with high efficiency.

Furthermore, in order to prevent a semiconductor substrate with ainsulating film such as a resist from being affected by charging, it isnecessary to apply a low accelerated electron beam of 2 keV or less.This technology is disclosed in the “Electron/Ion beam handbook (2ndedition),” edited by the 132nd Committee of Japan Society for thePromotion of Science, pp. 622-623, Nikkan Kogyo Shimbun (1986). However,the use of the low accelerated electron beam with a large currentgenerates aberrations due to the space charge effect, and therebyhigh-resolution observation has been difficult.

As a method for solving this problem, a technology wherein a highlyaccelerated electron beam is decelerated directly before a sample and isapplied to the sample substantially as a low-speed accelerated electronbeam is known. Such technology is disclosed in, for example, JP PatentPublication (Kokai) No. 2-142045 and JP Patent Publication (Kokai) No.6-139985.

With respect to an inspection apparatus using the above SEM, thefollowing problems have yet to be solved.

One problem is that detailed evaluation is impossible because thepresence of defects is digitally judged as being 0 or 1, and during thisperiod analog judgment cannot be performed. Taking a non-opening defectof a plug hole bottom as an example, this means that it isconventionally judged to be conductive or non-conductive, but incontrast there also exists an intermediate, semi-conductive state.However, a plug is originally required to permit low resistance andohmic connections among levels of wirings. In view of this point, it canbe said that a detailed analog evaluation should be conducted using theresistance.

Further, refresh defects of DRAMs, transistor leakage defects of flashmemories, or the like, though they are categorized as the same type ofelectric characteristic defects, are caused by a micro leakage currentof a pn junction, and these defects are difficult to detect even with anSEM inspection apparatus. JP Patent Publication (Kokai) No. 2002-9121discloses attempts to detect the above defects by intermittentlyapplying an electron beam in a condition where a junction is charged ina reverse biased state, and detecting the defect as an electricpotential contrast image using a state where the charge is relaxedthrough a junction leakage current.

However, in this method, since the irradiation of the electron beam atthe same location is repeated many times, it is necessary to move awafer in a step-and-repeat manner. Therefore, when stationary time of astage mechanism or time lost through stage control is taken intoconsideration, a problem arises, in which the throughput, evaluated interms of the time required for one semiconductor substrate,deteriorates.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the above points,and thus has an object of providing an inspection method and aninspection apparatus using an electron beam, which enables a highthroughput of more detailed and quantitative evaluation, by using an SEMinspection apparatus as technology for inspecting characteristicelectric defects that are difficult to detect through optical images andby making it possible not only to judge conductiveness ornon-conductiveness, etc., but also to measure the resistance or aleakage current amount at a pn junction.

An embodiment of the present invention is an inspection apparatus usingan electron microscope for detecting a defect on a pattern of a samplebased on a detection signal of secondary charged particles generated byscanning an electron beam, wherein a rough inspection for narrowing downdefect candidates is first conducted and defect review is performed, andthen the resistance or leakage amount of a defective portion ismeasured.

More specifically, a method of the present invention comprises the stepsof: irradiating, based on previously prepared information concerning adefect position on the surface of a sample, the defect and its vicinitywith an electron beam a plurality of times at predetermined intervals;detecting an electron signal secondarily generated from the samplesurface by the electron beam; imaging the electron signal detected bythe previously specified n-th or later electron beam irradiation; andmeasuring the resistance or a leakage amount of a defective portion ofthe sample surface in accordance with the degree of charge relaxation bymonitoring a charge relaxation state of the sample surface based oninformation of the electron beam image.

This specification includes part or all of the contents as disclosed inthe specification and/or drawings of Japanese Patent Application No.2002-180735, which is a priority document of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross sectional view showing a configuration of aSEM type visual inspection apparatus.

FIG. 2 is a function block diagram of an embodiment of the presentinvention.

FIG. 3 is a flow chart showing an inspection procedure.

FIG. 4 is a flow chart showing an inspection procedure.

FIG. 5 is a relationship diagram illustrating a principle for measuringthe resistance of a defective portion.

FIG. 6 is a plan view of a wafer holder.

FIG. 7 is a screen view showing an example display on a monitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed with reference to the accompanying drawings.

FIG. 1 is a vertical cross sectional view illustrating a configurationof an SEM type visual inspection apparatus 1 as one example of aninspection apparatus using a scanning electron microscope to which thepresent invention is applied. The SEM type visual inspection apparatus 1comprises an inspection chamber 2, the inside of which is evacuated, anda spare chamber (not shown in the present embodiment) for conveying asample substrate 9 into the inspection chamber 2. These inspectionchamber 2 and spare chamber are configured so that they areindependently evacuated. In addition to the above inspection chamber 2and spare chamber, the SEM type visual inspection apparatus 1 iscomposed of an image processing unit 5, a controller 6, and a secondaryelectrons detection unit 7.

The inside of the inspection chamber 2 is roughly divided into anelectron optics system 3, a sample chamber 8, and an optical microscopeunit 4. The electron optics system 3 comprises an electron gun 10, anelectron-beam drawing electrode 11, a condenser lens 12, a blankingdeflector 13, a scan deflector 15, a diaphragm 14, an objective lens 16,a reflecting plate 17, and an E×B deflector 18. A secondary electrondetector 20 of the secondary electrons detection unit 7 is disposedabove the objective lens 16 in the inspection chamber 2. An outputsignal of the secondary electron detector 20 is amplified by apreamplifier 21 provided outside the inspection chamber 2, which in turnis converted into digital data by an AD converter 22.

The sample chamber 8 comprises a sample table 30, an X stage 31, a Ystage 32, a position monitoring length-measuring device 34, and a samplesubstrate height measuring device 35. The optical microscope unit 4 islocated in the vicinity of the electron optics system 3 lying within theinspection chamber 2 and is installed at a position where they aredistant from each other to such an extent that they do not exertinfluence on each other. The distance between the electron optics system3 and optical microscope unit 4 is known. Further, the X stage 31 or theY stage 32 moves forward and backward alternately between the electronoptics system 3 and the optical microscope unit 4. The opticalmicroscope unit 4 comprises a light source 40, an optical lens 41, and aCCD camera 42.

The image processing unit 5 comprises a first image storage part 46, asecond image storage part 47, an operation part 48, and a defectdetermination part 49. A captured electron-beam image or optical imageis displayed on a monitor 50.

Operation instructions and operating conditions used for the respectiveparts of the apparatus are inputted to and outputted from the controller6. Conditions such as accelerating voltage, deflected width and adeflection speed of an electron beam at the occurrence of the electronbeam, timings for capturing signals by the secondary electrons detectionunit 7, a sample table traveling speed, and others have been inputted inadvance to the controller 6 so that they can be arbitrarily orselectively set depending on purposes. The controller 6 monitors shiftsor displacements in position and height from signals outputted from theposition monitoring length measuring device 34 and the sample substrateheight measuring device 35 by the use of the correction control circuit43. Based on the results of the monitoring, the controller 6 enables thecorrection control circuit 43 to generate a correction signal, and tosend the correction signal to the objective lens source 45 and a scansignal generator 44, so that an electron beam is always applied to theproper position.

In order to obtain an image of the sample substrate 9, a thinly-focusedelectron beam 19 is applied to the sample substrate 9 to thereby producesecondary electrons 51. They are detected in synchrony with the scanningof the electron beam 19 and the movements of the X stage 31 and the Ystage 32, thereby obtaining the image of the sample substrate 9.

It is essential to enhance the inspection speed for the SEM type visualinspection apparatus. Therefore, unlike an ordinary conventional type ofSEM, the SEM type visual inspection apparatus does not perform thescanning of an electron beam of an electron-beam current on the order ofpA at low speeds, perform the scanning a large number of times, orperform the superimposition of respective images on one another.Further, for the purpose of restricting charging on an insulatingmaterial, it is necessary to scan the electron beam once or severaltimes at high speed, rather than many times. Thus, in the presentembodiment, an electron beam having a larger current of, for example,100 nA, which is about 1,000 times or more greater than that of aconventional SEM, is scanned once alone to thereby form an image.

A diffusion refill-type thermofield emission electron source is used foran electron gun 10. The use of this electron gun 10 makes it possible toensure an electron beam current remains stable as compared with, forexample, a tungsten filament electron source and a cold field emissiontype electron source. Therefore, an electron beam image that showslittle change in brightness can be obtained. Further, since the electrongun 10 enables the electron beam current to be set at a high level, thehigh-speed inspection described below can be realized. The electron beam19 is drawn from the electron gun 10 by applying a voltage between theelectron gun 10 and the drawing electrode 11.

The electron beam 19 is accelerated by applying a negative potentialwith a high voltage to the electron gun 10. This enables the electronbeam 19 to move to the sample table 30 by means of energy equivalent tothe potential, followed by convergence on the condenser lens 12.Further, the electron beam 19 is thinly-focused by the objective lens 16to be applied to the sample substrate 9 mounted on the X stage 31 andthe Y stage 32 placed on the sample table 30. The sample substrate 9 isa semiconductor wafer, a chip, or a substrate having a micro-fabricatedcircuit pattern such as a liquid crystal, a mask, or the like. The scansignal generator 44 for generating a scan signal and a blanking signalis connected to the blanking deflector 13, and the objective lens source45 is connected to the objective lens 16.

To the sample substrate 9, negative voltage can be applied by ahigh-voltage power supply 36. By adjusting the voltage of thishigh-voltage power supply 36, the electron beam 19 is decelerated andelectron beam irradiation energy applied to the sample substrate 9 canbe adjusted to an optimum value without changing the potential of theelectron gun 10.

The secondary electrons 51 generated by applying the electron beam 19 tothe sample substrate 9 are accelerated under the negative voltageapplied to the sample substrate 9. The E×B deflector 18 is disposedabove the sample substrate 9. The deflector 18 is used for turning theorbit of secondary electrons by means of both electric and magneticfields without affecting the orbit of the electron beam 19. This enablesthe accelerated secondary electrons 51 to be deflected in apredetermined direction. The intensities of the electric and magneticfields applied to the E×B deflector 18 allow adjustments to the amountof deflection of secondary electrons. In addition, these electric andmagnetic fields can be varied in conjunction with the negative voltageapplied to the sample substrate 9.

The secondary electrons 51 deflected by E×B deflector 18 collide withthe reflecting plate 17 under predetermined conditions. The reflectingplate 17 has a conical shape and also has a function as a shield pipe toshield the electron beam 19 applied to the sample substrate 9. When theaccelerated secondary electrons 51 collide with this reflecting plate17, second secondary electrons 52, having energy from a few eV to 50 eV,are produced from the reflecting plate 17.

The secondary electrons detection unit 7 has the secondary electrondetector 20 provided within the evacuated inspection chamber 2. Apreamplifier 21, an AD converter 22, an optical converting means 23,optical transmission means 24, an electric converting means 25, ahigh-voltage power supply 26, a preamplifier drive source 27, an ADconverter drive source 28, and a reverse bias source 29 are providedoutside the inspection chamber 2, which constitutes the secondaryelectrons detection unit 7.

The secondary electrons detector 20 of the secondary electrons detectionunit 7 is placed above the objective lens 16 inside the inspectionchamber 2. The secondary electrons detector 20, preamplifier 21, ADconverter 22, optical converting means 23, preamplifier drive powersource 27, and AD converter drive power source 28 are rendered floatingat a positive potential by the high-voltage power supply 26. The secondsecondary electrons 52 generated from the collision of the secondaryelectrons 51 with the reflecting plate 17 are introduced into thesecondary electrons detector 20 under the action of a drawing electricfield created by the positive potential.

The secondary electrons detector 20 is configured so as to detect thesecond secondary electrons 52 generated by the collision of thesecondary electrons 51 with the reflecting plate 17 in conjunction withthe time when the electron beam 19 is scanned. An output signal of thesecondary electrons detector 20 is amplified by the preamplifier 21provided outside the inspection chamber 2, which in turn is convertedinto digital data by the AD converter 22.

The AD converter 22 is configured so as to convert an analog signaldetected by the secondary electrons detector 20 into a digital signalimmediately after the preamplifier 21 amplifies the signal, and thentransmit the signal to the image processing unit 5. Since the detectedanalog signal is digitized and transmitted immediately after itsdetection, a signal having a higher speed and S/N ratio than aconventional signal can be obtained.

The sample substrate 9 is mounted on the X stage 31 and the Y stage 32.Either one of a method for stopping the X stage 31 and the Y stage 32upon the execution of an inspection to thereby two-dimensionally scanthe electron beam 19, and a method for sequentially moving the X stage31 and the Y stage 32 in a Y direction at a constant speed upon theexecution of the inspection to thereby linearly scan the electron beam19 in an X direction can be selected. In the case of inspecting arelatively small specific given area, the former method of stopping thesample substrate 9 for inspection is effective. In the case ofinspecting a relatively wide area, the method of consecutively movingthe sample substrate 9 at a constant speed for inspection is effective.In addition, when blanking on the electron beam 19 is necessary, theelectron beam 19 is deflected by the blanking deflector 13 so that theelectron beam is controlled so as not to pass through the diaphragm 14.

In the present embodiment, a laser interference-based wavemeter is usedas the position monitoring length-measuring device 34 for monitoring thepositions of the X stage 31 and the Y stage 32. The positions of the Xstage 31 and the Y stage 32 can be monitored in real time, and theresults thereof are to be transferred to the controller 6. Further, thepresent embodiment is configured so that data items concerning thenumbers of revolutions of motors used for the X stage 31, Y stage 32,etc. are also transferred from their drivers to the controller 6 in thesame manner. The controller 6 is able to accurately grasp each area andposition irradiated with the electron beam 19 based on these data items.Therefore, when a position irradiated with the electron beam 19 isdeviated from an intended position, the correction control circuit 43can correct the position in real time, if necessary. Further, areasirradiated with the electron beam 19 can be stored for every samplesubstrate 9.

The sample substrate height measuring device 35 utilizes an opticalmeasuring instrument, e.g., a laser interference measuring instrument ora reflected-light type measuring instrument for measuring the positionchange of reflected light. It is configured so as to measure the heightof the sample substrate 9 mounted on the X stage 31 and the Y stage 32in real time. The present embodiment employs a method comprising thesteps of applying a slender white light transmitted through a slit tothe sample substrate 9 through a transparent window, detecting theposition of the reflected light thereof by a position detecting monitor,and calculating the amount of height change from the variation inposition. Based on data measured by this optical height measuring device35, the focal distance of the objective lens 16 is dynamicallycorrected, whereby the electron beam 19 that is focused on each area tobe inspected can be always applied. Further, warpage or heightdistortion of the sample substrate 9 is measured in advance before theapplication of the electron beam, and based on the data thereof, theobjective lens 16 may also be configured so that correction conditionsthereof are set for each inspected area.

The image processing unit 5 comprises a first image storage part 46, asecond image storage part 47, an operation part 48, a defectdetermination part 49 and a monitor 50. An image signal on the samplesubstrate 9 detected by the secondary electrons detector 20 is amplifiedby the preamplifier 21 and digitized by the AD converter 22. Thereafterit is converted into a light signal by an optical converting means 23and transmitted by an optical transmitting means 24. Then, it isconverted again into an electric signal by an electric converting means25, and the thus obtained signal is stored in the first or second imagestorage part 46 or 47. The operation part 48 performs an alignmentbetween the image signal stored in the first image storage part 46 andthe image signal stored in the second image storage part 47,standardization of signal level, and various image processes forremoving noise signals. It also computes both the image signals forcomparison. The defect determination part 49 compares the absolute valueof the differential image signal computed for comparison by theoperation part 48 with a predetermined threshold value. When the levelof the differential image signal is larger than the predeterminedthreshold value, the defect determination part 49 judges their pixels asdefect candidates, and their positions, the number of defects, etc. aredisplayed on the monitor 50.

Next, the operation of each part of the inspection apparatus shown inFIG. 1 will be described according to the inspection procedure shown inFIG. 3. FIG. 3 shows a flowchart of the inspection procedure.

First, a wafer cassette having a wafer placed on the desired shelf isplaced on a cassette placement part of a wafer transportation system(Step 310 of FIG. 3).

Next, in order to specify the wafer to be inspected, the number of thecassette shelf having the wafer placed thereon is entered through anoperation screen. Then, through the operation screen various inspectionconditions are inputted (Step 320 of FIG. 3). The inspection conditionparameters to be inputted include those involving electron beam current,electron beam irradiation energy, scanning speed and signal detectionsampling clock, the area to be inspected, and various types ofinformation regarding the wafer to be inspected. Further, the contentconcerning whether a plurality of wafers are to be automatically andcontinuously inspected one by one, whether one wafer is to be inspectedcontinuously under different conditions, or the like are inputted asinspection condition parameters. These parameters can be individuallyinputted, but usually the combinations of the above various inspectioncondition parameters are stored in a database as inspection conditiondata files. Therefore, it is necessary to select and input one fileamong inspection condition data files. When the input of theseconditions is completed (Step 320 of FIG. 3), the inspection starts(Step 330 of FIG. 3).

When automatic inspection starts, a predetermined wafer is firsttransported into the inspection apparatus. When wafers to be inspectedhave different diameters, or when wafers have different shapes fallingbetween those of the orientation flat type and notch type, the wafertransportation system can deal with these cases by replacing one holderfor placing a wafer with another in accordance with the sizes or shapesof wafers. The wafer to be inspected is transported from the wafercassette onto the wafer holder by the wafer loader, which includes anarm and a preliminary vacuum chamber. The wafer is securely held andsubjected to evacuation together with the holder inside the waferloader, and then transported to the inspection chamber that has alreadybeen evacuated by the evacuation system (Step 340 of FIG. 3). When thewafer is loaded, electron beam irradiation conditions for each part areset by an electron optics system controller based on the above inputtedinspection condition parameters.

FIG. 6 is a plane view of a wafer holder 750 on which a wafer 760 isplaced. The wafer holder 750 as shown in FIG. 6 has a beam calibrationpattern 770 placed thereon. A stage moves so that the beam calibrationpattern comes beneath the electron optics system (Step 350 of FIG. 3),and an electron beam image of the beam calibration pattern 770 isobtained for making focal and astigmatic adjustments according to theobtained image. Then, the stage moves further so that the electronoptics system is located above a specific point of the wafer to beinspected to obtain an electron beam image of the wafer and to adjust acontrast image or the like. At this time, when it is necessary to modifythe electron beam irradiation conditions, etc., the parameters aremodified and the beam calibration can be performed again. At the sametime the height of the wafer is obtained by the height detector, a waferheight detection system computes the correlation between the heightinformation and electron beam focusing conditions. Thereafter, wheneveran electron beam image is obtained, an automatic adjustment of thefocusing conditions is made based on the results of the wafer heightdetection, without the need for focusing each time. This enableselectron beam images to be obtained continuously and at high speeds(Step 360 of FIG. 3).

When the input of the electron beam irradiation conditions and thefocal/astigmatic adjustment are completed, alignment is performed inaccordance with two points on the wafer (Step 370 of FIG. 3).

After the alignment is completed, the rotation or coordinate values arecorrected based on the results of the alignment. Then, the stage movesso that the electron optics system is located above a second calibrationpattern 780 placed on the wafer holder 750 as shown in FIG. 6 (Step 380of FIG. 3). The second calibration pattern 780 is a transistor or apattern corresponding to a transistor having a normal junction formedthereon in advance. Using that pattern, the brightness of a normalportion is calibrated. Based on the results of the calibration, theelectron optics system is located above the wafer to obtain an image ofa pattern point on the wafer and perform brightness adjustment: in otherwords, calibration (Step 390 of FIG. 3).

After the calibration is completed, the inspection is performed (Step400 of FIG. 3). With respect to the inspection method, while the stageis continuously moved to conduct the inspection of specified areas, theimage processing is carried out on a real-time basis and an image of adefect occurrence point is automatically stored (Step 410 of FIG. 3).Then, the inspection result is displayed on the monitor 50, and the datais outputted to the outside through a data conversion part (Step 420 ofFIG. 3).

For inputting the inspection conditions (Step 320 of FIG. 3), when thecondition is set wherein one point is inspected several times underdifferent conditions, a charge elimination process is carried out on thearea that has been once inspected (Step 440 of FIG. 3). Although acharge-elimination part is not shown in FIG. 1, the charge eliminationprocess is carried out, for example, by the application of ultravioletlight.

Then, an inspection is carried out again under different electron beamirradiation conditions (Step 400 of FIG. 3). In this way, when theinspection is completed, the wafer is unloaded and the inspection isfinished (Step 430 of FIG. 3).

FIG. 2 is a function block diagram showing an embodiment of the presentinvention. The inspection performed in accordance with the inspectionprocedure described above is regarded as a rough inspection. Based onthe results of this rough inspection, defect candidates are narroweddown. Thereafter, detailed inspection as shown below is carried out.

Namely, the inspections performed and the output of results obtained atSteps 400, 410, and 420 of FIG. 3 are represented as defect information220 outputted from the image processing unit 5 in FIGS. 2 (a) and (b).Based on this defect information 220, defect position information 240 isgenerated by a defect position information generating unit 230. Thestage is moved so as to bring a defect position indicated by the defectposition information 240 underneath the electron optics system, and aresistance/leakage amount measuring unit 250 measures the resistance anda leakage amount 260 (detailed inspection).

Since the rough inspection of the entire wafer is conducted at highspeed by continuously moving the stage to narrow down defect candidates,and then a detailed inspection is conducted, which takes more time, theentire inspection efficiency can be greatly improved.

In FIG. 2(b), the stage is moved based on the defect positioninformation 240, and a defect is reviewed by a defect review processingunit 270. Thereafter, the resistance and leakage amount are measured.While doing this, defect candidates are further narrowed down by defectreview, and the inspection efficiency can be further enhanced.

FIG. 4 is a flow chart showing an inspection procedure. With referenceto FIG. 4, the inspection procedure shown in FIG. 2(b) is described indetail.

First, a wafer cassette having a wafer placed on a desired shelf isplaced on a cassette placement part of a wafer transportation system(Step 510 of FIG. 4).

Next, in order to specify a wafer to be inspected, the number of thecassette shelf having the wafer placed thereon is entered through anoperation screen. Then, through the operation screen the results of arough inspection previously conducted are inputted (Step 520 of FIG. 4).The input contents include file names storing the inspection results.

When the input is completed, a defect review starts (Step 530). Onceautomatic defect review starts, first the predetermined wafer istransported into the inspection apparatus and then transported to aninspection chamber that has been already evacuated by the evacuationsystem (Step 540 of FIG. 4).

When the wafer is loaded, the stage is moved so as to bring a defectposition underneath the electron optics system based on the defectposition information as the above inputted results of the roughinspection (Step 550). The defect is displayed on the monitor 50 forreviewing (Step 560).

Thereafter, the process is shifted to a resistance measurement mode(Step 600).

Next, the electron beam irradiation condition is tentatively set at Step610. Since the principle disclosed in JP Patent Publication (Kokai) No.2002-9121 described above is used for measurement, an electron beamcurrent amount, an XY scanning size, an irradiation interval, the numberof irradiation times, etc. are tentatively set. At Step 620, an imagecorresponding to these conditions is displayed, and it is judged whetherthese conditions are suitable for measurement at Step 630. If theconditions are not suitable, the process returns to Step 610 to adjustthe conditions. After suitable conditions are determined, the resistanceof the defective portion is measured at Step 640.

Thereafter, the resistance measurement mode is finished, and the resultsof review, the results of resistance measurement, or the like areoutputted at Step 570. With respect to subsequent defects, the sameprocesses are repeated. Then, after the processes for all the defectsare finished, the wafer is unloaded at Step 590 and then the process isfinished.

FIG. 5 is a relationship diagram illustrating a principle for measuringthe resistance of a defective portion. The horizontal axis representstime, and the vertical axis represents the amount of electron beamirradiation and charged voltage, or SEM image brightness. The detailedprinciple of a method for resistance measurement of a defective portionis disclosed in JP Patent Publication (Kokai) No. 2002-9121. FIG. 5shows an example plug having a shorter charge relaxation time than aplug having a pn junction with a normal electron beam irradiationinterval T_(int). In this case, after electron beam is applied aplurality of times, a difference between the normal plug 700 and leakagedefect plug 710 in SEM image brightness occurs as shown in the figure.When the difference is classified quantitatively, the degree of leakage,namely the resistance component, can be estimated. For example, when thedifference is larger, the resistance is estimated to be smaller.

FIG. 6 is a plane view of a wafer holder as mentioned above. Severaltypes of leakage samples generated from a normal pn junction areprepared in the second calibration pattern 780 provided on the waferholder 750, and these are compared with the SEM image brightness of eachdefective portion. This enables more accurate quantitative evaluation.By doing this, the estimation of absolute resistance can be achieved.

FIG. 7 is a screen view showing an example display on a monitor. Theexample display of FIG. 7 includes the measurement results concerningthe resistance of defects. On left side of a screen 800, a wafer map 810is displayed, and defects are indicated on the map by circular signs.Portions where leakage defects occur are indicated as a distributionpattern. In an area 820, legends for the distribution pattern of leakagedefective portions as shown in the wafer map 810 are displayed, and inthis example, the resistance is classified into three types. Each typemay be distinguished by color to easily and visually identify them. Inthe figure, “XX” and “YY” practically represent specific values of theresistance. These values can be arbitrarily set. Further, the conditionsat the time of measuring the resistance in this example are displayed inan area 830. An electron beam current amount, a scanning size in eachdirection of X or Y axis, an irradiation interval of the electron beam,and the number of times for electron beam irradiation on the same areaare displayed in an area 832, an area 834, an area 836, and an area 838,of the area 830, respectively.

Defects such as leakage defects are greatly affected by processconditions, and therefore, for example, some defects are likely to occuraround the wafer. According to this embodiment, such distributioncharacteristic can be more accurately grasped.

Although defects such as leakage defects are indicated on thedistribution on the wafer in this embodiment, they may be indicated as adistribution on each chip of the wafer. In this case, the wafer map 810as shown in FIG. 7 may display one chip or a plurality of chips.

The above embodiments according to the present invention are summarizedas follows.

A method is provided, which comprises the steps of: irradiating, basedon previously prepared information concerning a defect position on thesurface of a sample, the defect and its vicinity with an electron beam aplurality of times at predetermined intervals; detecting an electronsignal secondarily generated from the sample surface by the electronbeam; imaging an electron signal detected by the previously specifiedn-th or later electron beam irradiation; and measuring the resistance ora leakage amount of a defective portion of the sample surface inaccordance with the degree of charge relaxation by monitoring a chargerelaxation state of the sample surface based on the electron beam imageinformation.

The method may further comprise displaying image information obtained bythe imaging step.

Further, the previously prepared defect position information isgenerated based on defect inspection by continuously moving a samplestage having a wafer placed thereon. The electron beam irradiation step,electron signal detection step, and resistance/leakage amountmeasurement step are repeated in a state where the sample stage is movedsequentially and stopped at each defect position based on the defectposition information.

Furthermore, the resistance or leakage amount of each defective portionobtained in the resistance/leakage amount measurement step is displayedas in a map on a schematic diagram of the wafer organized by type ofdefect.

Moreover, a method is provided comprising the steps of: scanning anelectron beam on a wafer while continuously moving a sample table havingthe wafer placed thereon; detecting an electron signal secondarilygenerated from the wafer surface by the electron beam; imaging theelectron signal; specifying a defective portion by comparing electronbeam images having the same pattern with each other; generating defectposition information containing at least position information amongattribution information of the defective portion; irradiating the defectand its vicinity with the electron beam a plurality of times atpredetermined intervals based on the defect position information;detecting an electron signal secondarily generated from the wafersurface by the electron beam; imaging an electron signal detected by thepre-specified n-th or later electron beam irradiation; and measuring theresistance or a leakage amount of the defective portion on the wafersurface depending on the degree of charge relaxation by monitoring acharge relaxation state on the wafer surface in accordance with theelectron beam image information.

In addition, an inspection apparatus is provided, which comprises asample table for wafer placement; a stage mechanism unit forcontinuously moving the sample table; an electron source; an electronoptics system for applying and scanning an electron beam from theelectron source on the wafer; a detector for detecting an electronsignal secondarily generated from the wafer surface by the electronbeam; an image processing unit for imaging the electron signal andspecifying a defective portion by comparing electron beam images havingthe same pattern with each other; and a defect position informationgenerating unit for generating defect position information including atleast position information among attribute information of a defectiveposition. Here, the electron optics system has a function to irradiate,based on the defect position information, a defect and its vicinity withthe electron beam at predetermined intervals a plurality of times. Thedetector detects the electron signal secondarily generated from thewafer surface by the electron beam, and the image processing unit has afunction to image the electron signal detected by the pre-specified n-thor later electron beam irradiation. The apparatus further comprises aresistance/leakage amount measurement part for measuring the resistanceor a leakage amount of the defective portion on the wafer surfacedepending on the degree of charge relaxation by monitoring the chargerelaxation state of the wafer surface according to the electron beamimage information.

As described above, it is possible to obtain an inspection method and aninspection apparatus enabling more detailed and quantitative evaluationat a high throughput level, by using an SEM type inspection apparatus asa technology for inspecting electric characteristic defects that aredifficult to be detected by optical images, and making it possible notonly to judge conductiveness or non-conductiveness but also to measurethe resistance or a leakage current amount at a pn junction.

Effect of the Invention

As mentioned above, the present invention provides an inspection methodand an inspection apparatus using an electron beam, which enables moredetailed and quantitative evaluation at a high throughput level.

All publications, patents and patent applications cited herein areincorporated herein by reference in their entirety.

1. An inspection method using an electron beam comprising the steps of:irradiating, based on previously prepared information concerning adefect position on the surface of a sample, the defect and its vicinitywith an electron beam a plurality of times at predetermined intervals;detecting an electron signal secondarily generated from the samplesurface by the electron beam; imaging the electron signal detected bythe pre-specified n-th or later electron beam irradiation; and measuringthe resistance or a leakage amount of a defective portion of the samplesurface in accordance with the degree of charge relaxation by monitoringa charge relaxation state of the sample surface based on the electronbeam image information.
 2. The inspection method according to claim 1,wherein the method comprises displaying image information obtained bythe imaging step.
 3. The inspection method according to claim 1, whereinthe previously prepared defect position information is generated basedon defect inspection by continuously moving a sample stage having thesample placed thereon, and the electron beam irradiation step, electronsignal detection step, and resistance/leakage amount measurement stepare repeated in a state where the sample stage is moved sequentially andstopped at each defect position based on the defect positioninformation.
 4. The inspection method according to claim 1, wherein theresistance or leakage amount of each defective portion obtained in theresistance/leakage amount measurement step is displayed as in a map on aschematic diagram of the sample organized by type of defect.
 5. Aninspection method using an electron beam comprising the steps of:scanning an electron beam on a sample while continuously moving a sampletable having the sample placed thereon; detecting an electron signalsecondarily generated from the sample surface by the electron beam;imaging the electron signal; specifying a defective portion by comparingelectron beam images having the same pattern with each other; generatingdefect position information containing at least position informationamong attribution information of the defective portion; irradiating thedefect and its vicinity with the electron beam a plurality of times atpredetermined intervals based on the defect position information;detecting an electron signal secondarily generated from the samplesurface by the electron beam; imaging an electron signal detected bypre-specified n-th or later electron beam irradiation; and measuring theresistance or a leakage amount of the defective portion on the samplesurface depending on the degree of charge relaxation by monitoring thecharge relaxation state on the sample surface in accordance with theelectron beam image information.
 6. An inspection apparatus using anelectron beam comprising: a sample table for sample placement; a stagemechanism unit for continuously moving the sample table; an electronsource; an electron optics system for applying and scanning an electronbeam from the electron source on the sample; a detector for detecting anelectron signal secondarily generated from the sample surface by theelectron beam; an image processing unit for imaging the electron signaland specifying a defective portion by comparing electron beam imageshaving substantially the same pattern with each other; and a defectposition information generating unit for generating defect positioninformation including at least position information among attributeinformation of the defective position, wherein the electron opticssystem has further a function to irradiate, based on the defect positioninformation, a defect and its vicinity with the electron beam atpredetermined intervals a plurality of times, the detector detects theelectron signal secondarily generated from the sample surface by theelectron beam, the image processing unit has a function to image theelectron signal detected by the pre-specified n-th or later electronbeam irradiation, and the inspection apparatus further comprises aresistance/leakage amount measurement part for monitoring the chargerelaxation state of the sample surface according to the electron beamimage information and measuring the resistance or a leakage amount ofthe defective portion on the sample surface depending on the degree ofcharge relaxation.